Any discussion of the background art throughout the specification should in no way be considered as an admission that such background art is prior art, nor that such background art is widely known or forms part of the common general knowledge in the field.
The detection of substances posing chemical, biological and explosives (CBE) threats has become critical in recent years, for example, for airport security. Many advances in instrumentation designed for trace detection have been made to locate illicit compounds. A significant hindrance has been the requirement to measure compounds of interest given their low concentrations. Hence, significant interest has developed in techniques enhancing the signal from a species of interest while simultaneously reducing sensitivity to contaminants.
For use in such an application, cavity ringdown spectroscopy (CRDS) analysis systems and methods for analysing an absorbance signal are disclosed in International (PCT) Patent Application Publication No. WO 2012/021943 (PCT/AU2011/001071) published on 23 February in the name of NewSouth Innovations Pty Limited et al. In one aspect, the system comprises: a modulator, a light source, an optical cavity, a detector, a mixer, a signal transformer, a determiner module, and an analyser module. The modulator generates a modulation signal. The light source is adapted to be modulated using the modulation signal. The optical cavity resonates modulated light from the light source and outputs an absorbance signal. The detector detects the absorbance signal and generates a time-dependent detected signal. The mixer multiplies the detected signal with the modulation signal to generate a mixed signal. The signal transformer transforms the mixed signal and generates a Fourier transformed time-decay signal. The determiner module determines the magnitude of each transformed time-decay signal at the fundamental frequency and at least one frequency other than the fundamental frequency to generate several frequency-dependent magnitude signals. The analyser module analyses the frequency-dependent magnitude signals to determine data representative of the absorbance signal. This is done to determine the absorbance of a sample fundamental frequency and at a frequency other than the fundamental frequency. The system is able to analyse data quickly and is insensitive to noise sources that occur at frequencies other than those in the modulated light signal.